Among men, average hourly wages for blacks in 2015 were 31% lower than for whites, a decline from 22% in 1979, says the Economic Policy Institute, a Washington D.C. think tank focused on labor issues. Among women, the gap grew from just 6% in 1979 to 19% in 2015.

EPI notes that the trend has progressed in fits and starts. The gaps expanded in the 1980s but narrowed in the late 1990s. The latter period was a time when labor markets tightened, wages increased, and discriminating between white and black workers effectively became more expensive for employers, the report says. The gaps widened again in the 2000s, particularly among women first entering the workplace. In 2015, the gap among “new entrant” women was almost 11%.

The report blames discrimination for the ongoing gaps, noting that “observable” factors like experience or education can’t explain the disparities. In the period between 1985 and 1996, for example, it puts almost all the wage gap-growth down to “unobservable” factors. That point is backed by research showing that employers are more likely to accept job applications from people named “Greg” or “Emily” than from people named “Lakisha” and “Jamal.”

Most depressingly, getting a college degree doesn’t seem to help, relatively speaking. Wage gaps between blacks and whites with college degrees are almost as wide as those with less education. “It is wrong that as a society we send a message that you must get a college degree to obtain economic security, yet even then you will experience a sizable earnings disadvantage,” the report says.

The authors, EPI analyst Valerie Wilson and Rutgers University economist William Rodgers, call for better enforcement of anti-discrimination laws and for better statistics showing the effect of unobservable factors on wages at a local level. Better data might at least illuminate the problem, even if fixing it is a much bigger challenge.